When comparing Sennheiser IE80 vs Brainwavz M2, the Slant community recommends Sennheiser IE80 for most people. In the question“What are the best rugged and durable earbuds & IEMs that last?”Sennheiser IE80 is ranked 8th while Brainwavz M2 is ranked 9th. The most important reason people chose Sennheiser IE80 is:

The main reason to get the IE80 is the excellent soundstage that you won't get with cheaper earbuds. The soundstage is wide and balanced with instruments clearly separated, allowing you to easily identify their position. It creates a very immersive sound.
The sound signature is great overall with clarity across all ranges. Highs are loud and clear without sibilance. Mids are rich. The bass is slightly emphasized to add more dynamics to the sound, though it does bleed slightly into the midrange. Also, if you wish to make the bass really powerful you have the ability to turn it up even more with a dial on the side of the buds.

Pros

Pro

Audiophile-grade sound quality

The main reason to get the IE80 is the excellent soundstage that you won't get with cheaper earbuds. The soundstage is wide and balanced with instruments clearly separated, allowing you to easily identify their position. It creates a very immersive sound.

The sound signature is great overall with clarity across all ranges. Highs are loud and clear without sibilance. Mids are rich. The bass is slightly emphasized to add more dynamics to the sound, though it does bleed slightly into the midrange. Also, if you wish to make the bass really powerful you have the ability to turn it up even more with a dial on the side of the buds.

Pro

Built to last you a long time

IE80 earbuds use high-quality kevlar-reinforced cables with a thick rubber strain relief and the earpiece shells have brushed metal plating. A strong connector holds detachable cables in place. Additional strain reliefis added by the L-shaped plug. These earphones are built to last and if there are any issues with them, there's a 2 year warranty.

Pro

Comfortable for extended periods of time

IE80 earbuds aren't fatiguing and stay in your ear confidently. While they're designed to be worn over-ear, under-ear cable routing works as well. They're also low profile enough that you can lie on your side with them.

Pro

Solid noise isolation

Once you pick the eartips that best fit you, the isolation is solid overall with double flange eartips offering the best isolation followed by other foam eartips and then silicon eartips.

Pro

If something happens to the cable, you can replace it rather than buy a new pair

Replacement cables are around $20.

Pro

Lightweight and comfortable to wear

Despite being made out of metal, these in-ears are still fairly lightweight, so wearing them for long periods shouldn't be a problem. The included ear tips are also quite soft, providing good cushioning and seal.

Pro

Warm sounding with forward mids, smooth highs and deep bass

The highs of these headphones are not too sparkly or airy, yet still has good detail. This results in a smoother sound. Mids are forward and clear, while the bass has good depth without creeping up on the mids.

Overall, these headphones are quite fun to listen to and can work with pop, rock, hip-hop and even metal. These are not the best though if you tend to listen to music with a lot of detail and intricate parts like jazz or classical as these do not offer a high level of detail reproduction.

Pro

Durable and tangle-resistant cables

The M2's cable is braided and covered with a sleeving material, making it significantly more durable than other cables. It also makes it extra resistant to tangling.

Pro

Solid build quality

The ear pieces are made out of metal and have great fit and finish. Not only does this make them look great, but also gives them a premium feel.

Pro

Includes plenty of accessories

With the M2, you get 2 types of ear tips with three sizes each, a shirt clip to prevent the cable from moving around when worn and ear cable guides to help keep the headphones in place.

Cons

Con

Replacement cables are expensive as well

If you need to replace the cables, they retail for about $20.

Con

Rather expensive

While these are among the cheapest audiophile-grade earphones, they're still priced at $250. It's a serious investment. And for many, just not worth it.

Con

Highs may be lacking for some

The audio lacks sparkle in the higher frequency range, which may be disappointing for those looking for lots of detail reproduction in that range.

Con

No in-line microphone

Not really a con, as headphones are primarily for listening to music. However, this can be inconvenient when used with a smartphone and you have to take calls.